Head-mounted cameras, one of which is disclosed in Patent Reference 1, for example, have been proposed. The head-mounted cameras provide a hands-free capability when capturing an image, so that the user of the camera can capture the image while working on another task. In addition, Patent Reference 2 has proposed to move a capturing position of a capturing unit according to an eye-gaze position of the user. This prevents the capturing position from moving even though the user moves his or her head while capturing the image, and makes possible stable image capturing.
One of the techniques actually moving the capturing position accurately based on the eye-gaze position may be to detect a real-space eye-gaze position of the user with respect to a position on the input image obtained from the capturing unit, and to control the capturing position in order to center the detected eye-gaze position. The following Patent References 3 and 4 exemplify techniques of calibrating the eye-gaze position on the input image to the real-space eye-gaze position of the user.
Described in Patent Reference 3 is a technique to show on a display any given calibration pattern formed in plural dots, to obtain eye movement data in horizontal and vertical directions when the user looks at the dots, and to calculate a calibration parameter according to the data. Patent Reference 3 presents the following techniques for calculating the eye movement data; namely, a corneal-reflection technique, a technique to utilize the difference between a degree of reflection on cornea and that on sclera, a technique to use a contact lens, and the EOG (Electro-Oculography) technique using a generated potential between the cornea and the retina.
In a technique described in Patent Reference 4, plural targets are set as characteristic points on a view image in a surrounding space for preparation of a measurement. Then, a person to be measured wears an eye-camera to sequentially look at the targets. Coordinates as the characteristic points of the watched targets in the view image and coordinate of eye mark signals while the watching are associated each other to be sequentially stored in a table storing unit. When measuring, this correction table with the coordinate stored is used to correct the eye mark signals transmitted from the eye-camera.    Patent Reference 1: Japanese Examined Patent Application Publication No. 3-62356    Patent Reference 2: Japanese Unexamined Patent Application Publication No. 8-84280    Patent Reference 3: Description in Japanese patent No. 2615831    Patent Reference 4: Japanese Unexamined Patent Application Publication No. 62-176427